This invention relates generally to integrated circuits for radio frequency devices and particularly to advanced integrated circuits which use lower supply voltages and smaller device geometries.
As integrated circuits scale to smaller and smaller geometries and supply voltages continue to decrease, a number of technologies which rely on voltage differences have become increasingly more difficult to implement in an effective fashion. The use of smaller voltages means that the speed at which devices operate may be diminished.
As integrated circuits have scaled to smaller and smaller geometries, designers have been effective in reducing the power supply voltages which such devices utilize. While it is very advantageous to decrease the necessary power supply voltage, a number of problems arise with respect to the xe2x80x9conxe2x80x9d resistance when the supply voltage decreases. See L. A. Glasser and D. W. Dobberpuhl, The Design and Analysis of VLSI Circuits, (December 1985) published by Addison-Wesley Publishing Co. at page 108. The transistor linear region resistance is inversely proportional to the gate to source voltage or xe2x80x9cVGSxe2x80x9d less the threshold voltage or xe2x80x9cVTxe2x80x9d.
As the supply voltage is scaled to ever lower voltages, this voltage difference can be reduced significantly. In addition, the transistor saturation voltage scales as (VGSxe2x88x92VT) decreases. As the device geometry scales, transistors may also run into what is known as xe2x80x9cvelocity saturationxe2x80x9d. Thus, the voltage range where the transistor operates in the linear region becomes increasing narrow as geometries and supply voltages are scaled.
Radio frequency devices, as used herein, are integrated circuits that generate signals in the radio frequency range. Many of these devices include not only analog processing functions but logic functions as well. This is particularly true as integrated circuits advance to the point where both logic and analog processing are on the same integrated circuit. For example, if a cellular telephone were to be integrated into a single integrated circuit for cost reduction and increased performance reasons, an integrated microprocessor and analog radio frequency section may be included on the exact same integrated circuit.
Thus, in at least some analog radio frequency processing applications, it may be desirable to have the latest transistor technology which achieves the highest operating speed due to the higher transistor switching speeds. This generally means that the geometries for feature sizes of the integrated circuit elements must be scaled progressively smaller and smaller. At the same time, smaller geometries generally mean lower operating voltages. Thus, as the geometries of the transistors become smaller and more integrated circuit transistors are packed into the same unit area, the supply voltages are progressively decreasing. Lower supply voltages may be advantageous since not only are they amenable to ever smaller geometries, but they may also result in less power consumption. This may be a particular issue in battery powered devices.
However, a problem arises with respect to at least one component particularly utilized in connection with radio frequency devices. Radio frequency devices need a power amplifier which is capable of amplifying an input signal to substantially higher levels for transmission by these radio-frequency devices. Thus, a relatively compact portable device, as one example, needs to have a transmitter that is powerful enough to generate a radio frequency signal that can be received at a sufficient distance away to make the device useful.
Of course, with the latest transistor technologies, the available transistors may be relatively fast but they may also have relatively low voltage power supplies. Thus, the design of the power amplifier is relatively difficult because the power from the power amplifier is a function of the square of the supply voltage divided by the resistance. Thus, the lower the supply voltage, the less power that can be generated by the power amplifier. And even if the resistance of the smaller geometry integrated circuit is significantly less, a limit is reached with respect to the amplitude of the power that may be generated. Particularly since power is related to the square of the voltage, it is relatively important to provide sufficient voltage levels to increase power output from power amplifiers.
Thus, there is a need for a radio frequency integrated circuit device with both a power amplifier that can generate sufficient power and, at the same time, relatively high frequency, smaller geometry transistors.